Cliff Naylor
Newbie
I have a 88 1500 GMC truck 5.7 TBI which has an spark advance problem. I installed a new 5.7 motor back in 2010 and it has been working like a charm until it started running rough about a week ago. I checked the obvious, cracked or broken vacuum lines, intake manifold and or TBI gasket leaking. Everything looked good. I then checked the timing and found that it was set at 0 Deg. As if the timing wire was disconnected. I found that the ground internal t the ignition module was open. So I replaced the ign mod and that fixed that problem. Timing came back but is now very erratic. After re verifying base timing at 0 by disconnecting by-pass, I then re-plugged the by-pass connector together. Timing at idle was about 14 deg advance. Increasing the RPM moderately retarded the timing to 4 deg then went back up to about 18 at 2500 RPM. I'm thinking I should be getting about 30 ish deg of advance at 2500. I've checked all the wiring for opens and grounds and high resistances. Nothing.. and no codes. Parts that have just been replaced are, Distributor cap and rotor
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, Delco ign mod in dist, ESC mod, Knock Sensor and ECM. Still the same problem. Timing just wont advance more than 19 deg.
